#create a mouse callback function which is executed when a mouse event takes place. it gives us (x,y) for every mouse event.

import cv2

import numpy as np

#mouse callback function

def draw_circle(event,x,y,flags,param):

if event==cv2.EVENT_LBUTTONDBLCLK:

cv2.circle(img, (x,y), 100, (255,0,0), -1)

#create a black image, a window and bind the function to window

img=np.zeroes((512,512,3), np.uint8)

cv2.namedWindow('image')

cv2.setMouseCallback('image', draw_circle)

while(1):

cv2.imshow('image',img)

if cv2.waitKey(20) & 0xFF == 27:

break

cv2.destroyAllWindows()